Prior art golf balls comprise, in general, three types. The first type is the three piece wound ball wherein a vulcanized rubber string is wound under tension around a solid or semi-solid core, and thereafter enclosed in a sheath or covering of tough, protective material. A second prior art golf ball is a one-piece ball formed from a solid mass of moldable resilient material which has been cured to develop the necessary degree of hardness to provide utility. One-piece molded balls do not have an enclosing cover. A third prior art ball is the two-piece ball that includes a solid core and a cover thereon.
The one-piece ball is formed from a combination of materials such as elastomers, fillers and curing agents which are molded under high pressure and temperature to provide a ball of suitable hardness and resilience. One-piece balls are described, for example, in U.S. Pat. No. 3,313,545, U.S. Pat. No. 3,373,123 and U.S. Pat. No. 3,384,612.
While the wound ball has for many years satisfied both the standards of the U.S.G.A. and most golfers, it has several disadvantages. For example, a wound ball is difficult to manufacture due to the number of production steps required and the careful control which must be exercised in each stage of manufacture to achieve suitable roundness, velocity or rebound, "click" and the like. "Click" is the term applied to the sound produced by the ball when dropped on a hard surface or when struck with a golf club. In addition, the cover material for the wound ball has not provided the optimum in adhesion to the wound core and is susceptible to cutting when struck by a golf club.
One-piece and two-piece golf balls, in contrast to wound golf balls, can be produced with an essentially perfect center of gravity and thus, exhibit excellent aerodynamic properties, superior roll and trueness of flight. Such golf balls are highly resistant to cutting and are practically indestructible during use in normal play. These balls return to round even when severely distorted and maintain their superior flight characteristics after extended use. Further, one and two-piece unitary golf balls can be manufactured with better quality than conventional wound balls. One-piece balls also maintain their playing characteristics throughout wide temperature ranges, possess an excellent shelf life, and do not water log. Moreover, if paint on one-piece golf balls becomes worn or damaged, the one-piece balls may be reclaimed by removing or stripping off the old paint and repainting. In contrast, wound balls seldom last long enough to allow repainting.
Although one-piece balls have several distinct advantages, they have not had satisfactory durability due to brittleness. Most one-piece balls do not survive more than about 1000 hits. A need therefore exists for one-piece balls which have high hardness but yet possess improved durability and flexibility to minimize cracking.